Straddling the scenic Montana-Idaho border, the Cabinet Gorge Hydroelectric Development on the Clark Fork River was built in 1952 to generate power for the Northwest. It has a significant influence on the local environment and economy. Schnabel was selected as the Independent Consultant for the 2017 Part 12 inspection, with Tom Fitzgerald serving as Co-Independent Consultant.
The facility includes a 208-foot-high, 395-foot-long variable radius concrete arch spillway, with a 164-foot-long left nonoverflow thrust block and 45-foot right non-overflow thrust block. A 112.5-foot-long concrete gravity wing dam ties the left end of the dam to a saddle dike (a concrete gravity section with buttressing earth fill) at the left abutment. There is an intake structure, four power tunnels, and a powerhouse located on the right abutment. The arch section contains eight vertical lift spill gates, each 35 feet high and a net width of 40 feet.
In accordance with our scope of services, we performed a field inspection of the facility and PFMA review workshop. During the PFMA review workshop, PFMs associated with the original diversion tunnels were discussed, and it was deemed appropriate to have these tunnels inspected during this Part 12 assessment. The deliverables included a supplemental memo from the review of the PFMA and a Part 12 Independent Safety Report.